1. Field of the Invention
The present invention relates to a two-dimensional image detector which detects a two-dimensional distribution of radial or electromagnetic rays such as particle rays, x-rays, visible light, infrared light, etc., (hereinafter referred as radial rays) as an image, and is used for a medical radial imaging apparatus, an industrial nondestructive inspection apparatus etc.
2. Description of the Related Art
In a two dimensional image detector, an active matrix substrate is integrated with an image sensor for converting radial rays to electric charge signals and a base board. The base board loads an electronic circuit including IC elements such as a small-signal amplifier for the electric charge signals, a control circuit, a gate driver circuit, a signal processing circuit, a power supply circuit, etc., thereon. The active matrix substrate integrated with the image sensor and the base board is fixed detachably to a case. A glass plate is used as the material of the active matrix substrate, whereas an aluminum plate is used as the material of the base plate. In the structure mentioned above, all the members are provided on the base board which holds the active matrix substrate and unitized, and the case serves as a cover of the unit.
Further, in order to shield the IC elements constituting the control circuit, the gate driver circuit, the signal processing circuit, the power supply circuit, etc. from the radial rays and assure their life duration, a sheet-shaped radiation shielding plate such as lead plate (Pb plate) is attached to a back surface side of the active matrix substrate (which is the opposite side of the surface where the image sensor is disposed) (See JP-A-2003-014862). In this structure, in order to prevent the active matrix substrate, which is integrated with the radiation shielding plate of heavy weight, from deformation or destruction, the thickness of the active matrix substrate or the base board integrated with the active matrix substrate needs to be thickened for the sake of mechanical strength required to the active matrix substrate. In such a case, a first base board (hereinafter referred as a reinforcing board), a radiation shielding plate, a second base board (hereinafter referred as a base board) and the electronic circuit including IC elements are attached to the back surface of the active matrix substrate in this order. Alternatively, a base board having a built-in radiation shielding plate is attached to the back surface of the active matrix substrate, and then the electronic circuit including IC elements is attached the back surface of the base board.
The structure of the related-art two-dimensional image detector will be descried below with reference to FIG. 3. An image sensor 1 which converts radial rays to electric charge signals is attached to an active matrix substrate 2. The active matrix substrate 2 is attached to a reinforcing board 3. A Pb plate 4 is attached to a back surface of the reinforcing board 3 as a radiation shielding plate. In order to support the weight of the Pb plate 4 and prevent the active matrix substrate 2 from deformation, the Pb plate 4 is sandwiched and hold between the reinforcing board 3 and a base board 5 without deformation, and integrated with the active matrix substrate 2. On side surfaces of the base board 5, a small-signal amplifier 6 and a gate driver 8 are formed, and on the back surface of the base board 5, a gate driver control circuit substrate 9, a signal processing and control circuit substrate 10 and a power supply substrate 11 are formed. Further, a pair of small-signal amplifier control substrates 7 are surely fixed to both end portions of the back surface of the base board 5 by a metallic fixing part, which is not shown in the figure. The small-signal amplifier control substrate 7 has a small-signal amplifier control circuit and the like, which are mounted thereon.
An output signal line output from the image sensor 1 through the active matrix substrate 2 is connected electrically to the small-signal amplifier 6. The lower portion of the small-signal amplifier 6 is bent toward the back surface of the base board 5, and connected electrically to the control circuit of the small-signal amplifier control substrate 7 and the electronic circuits of the signal processing and control circuit substrate 10 and the power supply substrate 11 formed on the back surface of the base board 5. Further, the lower portion of the gate driver 8 for supplying a read signal to the image sensor 1 is bent toward the back surface of the base board 5, and connected electrically to the gate driver control circuit substrate 9. The assembly of the above-described functional components constitutes a sensor section S, and the sensor section S is fixed detachably to a case 12 in a state such as screwed thereto. The back surface of the case 12 is closed by a back plate 13 after the sensor section S being fixed and electrically connected.
However, the above explained structure of related-art two-dimensional image detector has a problem of the life duration of the IC elements provided on the back surface of the base board 5 being shortened, disadvantage in assembling and difficulty in carrying and preserving (hereinafter referred to as handling) the active matrix substrate 2 especially when the active matrix substrate is a large type. More precisely, heat generated from such as small-signal amplifier 6 or IC elements is conducted to the image sensor 1 by the heat conduction. The image sensor 1 generally gets strongly affected by heat and thus, such the heat conduction is not preferable in terms of life duration and performance of the image sensor 1. Further, fine assembling work such as fixing and electrically connecting the small-signal amplifier control substrate 7 to the base board 5 from the back surface of the heavy sensor section S containing the Pb plate 4, and further bending the small-signal amplifier 6 so as to be connected to the small-signal amplifier control substrate 7 or the circuit placed on the back surface of the base board 5 is required. Although some adjunctive tools and jigs are used because of such a complex assembling work, workability of which is bad in that it results in increasing of working time due to the strain from a careful operation not to hurt oneself or not to damage the components by error during the operation. In addition, the sensor section S having precision components has a difficulty in handling due to its several ten kilograms of weight and a carefulness required when carrying and preserving without a cover.